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// Copyright 2020 Parity Technologies
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#![no_std]

use core::hash::Hasher;

use crunchy::unroll;

/// Hasher that just takes 8 bytes of the provided value.
/// May only be used for keys which are 32 bytes.
#[derive(Default)]
pub struct PlainHasher {
	prefix: u64,
}

impl Hasher for PlainHasher {
	#[inline]
	fn finish(&self) -> u64 {
		self.prefix
	}

	#[inline]
	fn write(&mut self, bytes: &[u8]) {
		debug_assert!(bytes.len() == 32);
		let mut prefix_bytes = self.prefix.to_le_bytes();

		unroll! {
			for i in 0..8 {
				prefix_bytes[i] ^= (bytes[i] ^ bytes[i + 8]) ^ (bytes[i + 16] ^ bytes[i + 24]);
			}
		}

		self.prefix = u64::from_le_bytes(prefix_bytes);
	}
}

#[cfg(test)]
mod tests {
	use super::*;

	#[test]
	fn it_works() {
		let mut bytes = [32u8; 32];
		bytes[0] = 15;
		let mut hasher = PlainHasher::default();
		hasher.write(&bytes);
		assert_eq!(hasher.prefix, 47);
	}
}